Radio wave reception device, radio wave clock, and repeater

ABSTRACT

A received low-frequency standard radio wave, which is an amplitude modulation signal, is converted to an intermediate frequency signal Sa, and is output to a detection circuit and an AGC circuit. The detection circuit and AGC circuit generates an RF control signal Sf 1  and IF control signal Sf 2  from the input intermediate frequency signal Sa, and controls an RF control circuit and IF control circuit by outputting the generated RF control signal Sf 1  and IF control signal Sf 2  to the RF control circuit and IF control circuit. By this a radio wave reception device can speed up AGC operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of application Ser. No.10/831,642 filed Apr. 23, 2004, now U.S. Pat. No. 7,215,937 which is aContinuation-in-Part Application of International Application No.PCT/JP03/13257 filed Oct. 16, 2003. This application is also based uponand claims the benefit of priority from the prior Japanese PatentApplication No. 2002-301897, filed Oct. 16, 2002, Japanese PatentApplication No. 2002-309733, filed Oct. 24, 2002, Japanese PatentApplication No. 2003-343534, filed Nov. 27, 2002, Japanese PatentApplication No. 2003-030857, filed Feb. 7, 2003, and Japanese PatentApplication No. 2003-030868, filed Feb. 7, 2003. The entire contents ofall of said prior applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a radio wave reception device, radiowave clock, and repeater.

BACKGROUND ART

Nowadays, low-frequency standard radio wave containing time data (thatis, a time code) are transmitted in various countries (for example,Germany, the United Kingdom, Switzerland, Japan, and so forth). InJapan, 40-kHz and 60-kHz low-frequency standard radio wave that havebeen subjected to amplitude modulation using a time code having a formatshown in FIG. 11, are transmitted from two transmission facilities(located in Fukushima Prefecture and Saga Prefecture). The time codecomprises a plurality of frame is defined to have a time cycle of 60seconds. According to FIG. 11, the time code is transmitted in a frameevery time the figure representing the minute of an accurate time isupdated (that is every minute).

A radio wave clock that receives a time code, and corrects time data ofa time circuit by the time code, is known. In this kind of radio waveclock, there is comprised an AGC (Auto Gain Control) circuit thatcontrols a gain of an amplification circuit, according to the intensityof the signal level after the amplification of the signal, output fromthe amplification circuit, so that the precise time can be corrected inan internal circuit even though the signal level of the received radiowave fluctuates.

In this AGC circuit, gain control of the amplification circuit wascarried out by filtering the amplified signal. Therefore, a filterhaving a large enough time constant than the cycle of the modulationsignal. Namely, because the cycle of the low-frequency standard radiowave is one second, a filter with a large time constant is necessary,and by this, a problem of a large delay until the transient operation ofthe AGC circuit becomes constant, occurs.

Furthermore, at a stage of actually constructing the whole circuit, thecircuit needs to be designed, taking into consideration, several tens ofseconds of delay, to prevent occurrence of ripples. By this, reductionin delay by contriving the filter included in the AGC circuit, namely,speeding up the AGC operation is difficult.

In a case where a weak radio wave is received by the radio wavereception device, it is difficult to carry out stable detection, due tonoise, etc. included in the radio wave.

Furthermore, it is general that a filter for emitting noise is appliedwhen carrying out detection for radio waves. Because a filter has aconstant pass band, the filter allows noise components that are close tothe frequencies that are to be allowed to pass through, to also passthrough. If the pass band is narrowed, time delay occurs, and effectedthe signal processing, etc., thereafter.

DISCLOSURE OF INVENTION

One object of the present invention is to speed up the AGC operation inthe radio wave reception device, etc.

Another object of the present invention is to provide a radio wavereception device that can stably receive weak radio waves.

Still another object of the present invention is to provide a radio wavereception device and radio wave clock, that reduces noise and delaytime.

BRIEF DESCRIPTION OF DRAWINGS

These objects and other objects and advantages of the present inventionwill become more apparent upon reading of the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a diagram showing the circuit structure of a radio wave clock;

FIG. 2 is a block diagram showing the circuit structure of the radiowave reception device, of the first and second embodiment;

FIG. 3 is a block diagram showing the circuit structure of the detectioncircuit and AGC circuit, of the first embodiment;

FIG. 4 is a flow chart showing the processing of the radio wavereception device of the first embodiment;

FIG. 5A is a diagram showing the outline wave shape of a signal in theradio wave reception device of the first embodiment;

FIG. 5B is a diagram showing the outline wave shape of a signal Sb inthe radio wave reception device of the first embodiment;

FIG. 5C is a diagram showing the outline wave shape of a signal Sc inthe radio wave reception device of the first embodiment;

FIG. 5D is a diagram showing the outline wave shape of a signal Sd inthe radio wave reception device of the first embodiment;

FIG. 5E is a diagram showing the outline wave shape of a signal Se inthe radio wave reception device of the first embodiment;

FIG. 6 is a block diagram showing the circuit structure of the detectioncircuit and the AGC circuit of the second embodiment;

FIG. 7 is a flow chart showing the processing of the radio wavereception device of the second embodiment;

FIG. 8A is a diagram showing the outline wave shape of the signal Sathat goes through the radio wave reception device of the secondembodiment;

FIG. 8B is a diagram showing the outline wave shape of the signal Sbthat goes through the radio wave reception of the second embodiment;

FIG. 8C is a diagram showing the outline wave shape of the signal Sd1that goes through the radio wave reception device of the secondembodiment;

FIG. 8D is a diagram showing the outline wave shape of the signal Sd2that goes through the radio wave reception device of the secondembodiment;

FIG. 8E is a diagram showing the outline wave shape of the signal Sethat goes through the radio wave reception device of the secondembodiment;

FIG. 9 is a block diagram showing the circuit structure of a repeater ofthe seventh and ninth embodiment;

FIG. 10 is a block diagram showing the detection circuit and AGCcircuit, as a modification example of the first and second embodiment;

FIG. 11 is a diagram showing a time code of a low-frequency standardradio wave;

FIG. 12 is a block diagram showing the radio wave reception device ofthe third embodiment;

FIG. 13 is a block diagram showing the detection circuit and AGC circuitof the third embodiment;

FIG. 14 is a flow chart showing the processing of the radio wavereception device of the third embodiment;

FIG. 15A is a diagram showing the outline wave shape of the signal Sa inthe radio wave reception device of the third embodiment;

FIG. 15B is a diagram showing the outline wave shape of the signal Sb′in the radio wave reception device of the third embodiment;

FIG. 15C is a diagram showing the outline wave shape of the signal Sc inthe radio wave reception device of the third embodiment;

FIG. 15D is a diagram showing the outline wave shape of the signal Sd inthe radio wave reception device of the third embodiment;

FIG. 15E is a diagram showing the outline wave shape of the signal Se inthe radio wave reception device of the third embodiment;

FIG. 15F is a diagram showing the outline wave shape of the signal Sf inthe radio wave reception device of the third embodiment;

FIG. 16 is a circuit block diagram of the radio wave reception device ofthe fourth embodiment;

FIG. 17 is a circuit block diagram showing the detection circuit and AGCcircuit of the fourth embodiment;

FIG. 18A is a diagram showing the wave shape of the signal Sa in theradio wave reception device of the fourth embodiment;

FIG. 18B is a diagram showing the wave shape of the signal Sb in theradio wave reception device of the fourth embodiment;

FIG. 18C is a diagram showing the wave shape of the signal Sc in theradio wave reception device of the fourth embodiment:

FIG. 18D is a diagram showing the wave shape of the signal Sd in theradio wave reception device of the fourth embodiment;

FIG. 18E is a diagram showing the wave shape of the signal Se in theradio wave reception device of the fourth embodiment;

FIG. 19 is circuit block diagram of the detection circuit and the AGCcircuit of the fifth embodiment;

FIG. 20 is a circuit block diagram of the detection circuit and the AGCcircuit of the sixth embodiment;

FIG. 21 is a circuit block diagram showing a modification example of theradio wave reception device;

FIG. 22 is a circuit block diagram showing a modification example of theradio wave reception device;

FIG. 23 is a circuit block diagram of the radio wave reception device ofthe eighth embodiment;

FIG. 24 is a circuit block diagram of the signal reproduction circuit ofthe eighth embodiment,

FIG. 25A is a diagram showing the wave shape of the signal Sa in theradio wave reception device of the eighth embodiment;

FIG. 25B is a diagram showing the wave shape of the signal Sb in theradio wave reception device of the eighth embodiment;

FIG. 25C is a diagram showing the wave shape of the signal Sc in theradio wave reception device of the eighth embodiment;

FIG. 25D is a diagram showing the wave shape of the signal Sd in theradio wave reception device of the eighth embodiment;

FIG. 25E is a diagram showing the wave shape of the signal Se in theradio wave reception device of the eighth embodiment;

FIG. 25F is a diagram showing the wave shape of the signal Sf in theradio wave reception device of the eighth embodiment;

FIG. 26 is a flowchart showing the operations of the signal reproductioncircuit of the eighth embodiment;

FIG. 27 is a circuit block diagram of the radio wave reception device ofthe tenth embodiment;

FIG. 28 is a circuit block diagram of the signal reproduction circuit ofthe tenth embodiment;

FIG. 29 is a circuit block diagram of the signal reproduction circuit ofthe eleventh embodiment;

FIG. 30 is a circuit block diagram of the signal reproduction circuit ofthe twelfth embodiment;

FIG. 31 is a circuit block diagram of the signal reproduction circuit ofthe thirteenth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be described below withreference to the drawings. In the embodiments of the present invention,a case where the present invention is applied to a radio wave clock anda translator will be described. However, the present invention is notlimited to a radio wave clock and a repeater, and any device thatreceives a radio wave can be applied.

First Embodiment

First, the first embodiment of the present invention will be describedbelow with reference to FIGS. 1 to 5E.

FIG. 1 is a diagram showing an example of a circuit structure of a radiowave clock 1, of this embodiment. According to FIG. 1, the radio waveclock 1 comprises a CPU (Central Processing Unit) 10, an input unit 20,a display unit 30, a RAM (Random Access Memory) 40, a ROM (Read OnlyMemory) 50, a reception control unit 60, a timekeeping circuit 80, anoscillation circuit 81, and a time code conversion unit 70. Each unitexcept for the oscillation circuit unit 81 is connected to a bus B. Theoscillation circuit 81 is connected to the timekeeping circuit 80.

The CPU 10 reads out various programs stored in the ROM 50 at apredetermined timing or in accordance with an operation signal or thelike input from the input unit 20, and develops the read-out programs inthe RAM 40 in order to give instructions and supply data to each unit.Particularly, the CPU 10 performs various control, such as controllingthe reception control unit 60 at every predetermined interval to performan operation for receiving a standard radio wave, correcting datarepresenting a current time which is kept by the timekeeping circuit 80based on a standard time code input by the time code conversion unit 70,and outputting a display signal based on the corrected current time datato the display unit 30 to make the displayed time updated.

The input unit 20 comprises switches for controlling the radio waveclock 1 to perform various functions. When any of these switches isoperated, an operation signal is output to the CPU 10.

The display unit 30 is constituted by a compact liquid crystal displayor the like, and digitally displays data from the CPU 10, for example,the current time data kept by the time keeping circuit 80.

The RAM 40 stores the data processed by the CPU 10, and outputs thestored data to the CPU 10, under the control of the CPU 10.

The ROM 50 mainly stores system programs and application programsrelating to the radio wave clock 1.

The reception control unit 60 comprises a radio wave reception device61. The radio wave reception device 61 cuts off unnecessary frequencycomponents from a low-frequency standard radio wave received by anantenna to pick out a targeted frequency signal and converts and outputsthe target frequency signal to an intermediate frequency signal.

The timekeeping circuit 80 counts signals input from the oscillationcircuit 81, and obtains the current time data and the like. Thetimekeeping circuit 80 outputs the obtained current timed data to theCPU 10. The oscillation circuit 81 outputs a signal having a constantfrequency all the time.

The time code conversion unit 70 generates a standard time codeincluding data necessary to function as a clock, such as a standard timecode, a count-up code, a day code, etc., based on the signal output fromthe radio wave reception device, and outputs the generated standard timecode to the CPU.

FIG. 2 is a block diagram showing a circuit structure of the radio wavereception device 61 employing a super heterodyne type according to thefirst embodiment. According to FIG. 2, the radio wave reception device61 comprises an antenna ANT, an RF amplifier circuit 611, filtercircuits 612, 615, 617, a frequency conversion circuit 613, a localoscillation circuit 614, an IF amplifier circuit 616, an AGC (Auto GainControl) circuit 618, and a detection circuit 620.

The antenna ANT can receive low-frequency standard radio wave, and isconstituted by, for example, a bar antenna. A received radio wave isconverted into an electric signal and then output.

The electric signal output from the antenna ANT, and an RF controlsignal Sf1 output from the AGC circuit 618, are input to the RFamplifier circuit 611. The RF amplifier circuit 611 amplifies, andoutputs the electric signal input from the antenna ANT, in accordancewith the RF control signal Sf1.

The signal output from the RF amplifier circuit 611 is input to thefilter circuit 612. The filter circuit 612 allows a predetermined rangeof frequencies to pass through, relating to the input signal, i.e.outputs the signal, cutting off frequency components that are outsidethe range.

The signal output from the filter circuit 612, and the signal outputfrom the local oscillation circuit 614 is input to the frequencyconversion circuit 613. The frequency conversion circuit 613 mixes thetwo signals that are input, and outputs the signals as an intermediatefrequency signal. The local oscillation circuit 614 generates andoutputs the signal of the local oscillation frequency.

The intermediate frequency signal output from the frequency conversioncircuit 613 is input to the filter circuit 615. Then, the filter circuit615 allows signal components having frequencies of a predetermined rangeto pass through, where the intermediate frequency of the intermediatefrequency signal is placed in the center, i.e. outputs the signalcutting off the frequency components that are out of the range.

The signal output from the filter circuit 616 and an IF control signalSf2 output from the AGC circuit 618 is input to the IF amplifiercircuit. The IF amplifier circuit 616 amplifies and outputs the signalinput from the filter circuit 615 m in accordance with the IF controlsignal Sf2.

The signal output from the IF amplifier circuit 616 is input to thefilter circuit 617. Then, the filter circuit 617 allows signalcomponents having a predetermined range of frequencies to pass through,relating to the input signal, i.e. outputs the signal Sa, cutting offfrequency components that are out of the range.

The detection circuit 620 comprises a carrier extraction circuit 621 anda signal reproduction circuit 622.

The carrier extraction circuit is comprised of for example a PLL (PhaseLocked Loop) circuit. The signal Sa, output from the filter circuit 617,is input to the carrier extraction circuit 621. Then, a signal Sbwherein the signal level is a fixed standard signal that has the samefrequency and phase of signal Sa, is output.

The signal Sa output from the filter circuit 617, and the signal Sboutput from the carrier extraction circuit 621 are input to the signalreproduction circuit 622. Then, the signal reproduction circuit 622outputs a signal Sc and a signal Sg, that corresponds to a basebandsignal of signal Sa (namely, the signal that reproduces the signal Sa).

The signal Sa output from the filter circuit 617, and the signal Scoutput from the signal reproduction circuit 622 are input to the AGCcircuit 618. The AGC circuit 618 outputs RF control signals f1 and f2that control the amplification of the gain of the RF amplifier circuit611 and IF amplifier circuit 616, in accordance with the intensity(signal level) of the signal Sa.

FIG. 3 is a circuit block diagram showing an example of the circuitstructure of the AGC circuit 618 and the detection circuit 620 thatconstitutes the radio wave reception device 61. According to FIG. 3, thecarrier extraction circuit 621 comprises a PD (Phase Detector) 621 a, anLPF (Low Pass Filter) 621 b, and an oscillator 621 c.

The signal Sa output from the filter circuit 617 and the signal outputfrom the oscillator 621 c are input to the PD 621 a. The PD 621 acompares the phases of the two input signals, and outputs aphase-difference signal having a signal level corresponding to thedetected phase difference.

The phase-difference signal output from the PD 621 a, is input to theLPF 621 b. The LPF 621 b allows signal components having frequencies ofa predetermined low frequency range (low pass) to pass through, i.e.outputs the signal, cutting off the frequency components that are out ofthe range.

The signal output from the LPF 621 b is input to the oscillator 621 c.The oscillator 621 c adjusts the oscillation frequency difference of thesignal that is to be amplified, based on the input signal, so that thephase of the signal that is to be amplified becomes the same phase asthe signal Sb of the carrier. After the adjustment, the oscillator 621 coutputs the adjusted signal as signal Sb.

The signal reproduction circuit 622 comprises a multiplier 622 a, andLPFs 622 b, 622 c.

The signal Sa output from the filter circuit 617 and the signal Sboutput from the oscillator 621 c are input to the multiplier (mixer) 622a. The multiplier 622 a multiplies the signal Sa and the signal Sb, andoutputs the multiplied signal as Sc.

The signal Sc output from the multiplier 622 a is input to the LPF 622b. The LPF 622 b allows a predetermined range (low pass) of frequenciesof the signal Sc to pass through, i.e. outputs a signal Sc′ that cutsoff the frequency components that are out of the range. By the LPF 622b, the high frequency components of the signal Sa is cut off, and asignal (reproduced signal) that is nearly equal to the baseband signalof signal Sa is gained.

The signal Sc′ output from the LPF 622 b is input to the LPF 622 c.Then, the LPF 622 c allows a predetermined range (low pass) offrequencies, relating to the signal Sc′, and outputs a signal Sg thatcuts off the frequency components that are out of the range. The signalSg corresponds to the data signal of the low-frequency standard radiowave (reproduced signal) gained by the radio wave reception device 61.

The AGC circuit 618 comprises an inverting amplifier 618 a, a multiplier618 b, an AGC detection circuit 618 c, an LPF 618 d, and an AGC voltagegeneration circuit 618 e.

The signal Sc′ output from the LPF 622 b is input to the invertingamplifier 618 a. The inverting amplifier 618 a inverts and amplifies thesignal Sc′ and outputs the inverted and amplified signal as signal Sd.

The signal Sa output from the filter circuit 617 and the signal Sdoutput from the inverting amplifier 618 a are input to the multiplier618 b. Then, the multiplier 618 b multiplies the signal Sa and signalSd, and outputs the multiplied signal as signal Se.

The signal Se output from the multiplier 618 b is input to the AGCdetection circuit 618 c. Then, the AGC detection circuit 618 c detectsthe input signal Se (for example, by peak detection), and outputs asignal after detection.

The signal output from the AGC detection circuit 618 c is input to theLPF 618 d. Then, the LPF 618 d allows signal components having apredetermined range (low pass) of frequencies, relating to the inputsignal, to pass through, i.e. outputs a signal, cutting off thefrequencies that are out of the range.

The signal output from the LPF 618 d is input to the AGC voltagegeneration circuit 618 e. Then, in accordance with the input level ofsignal, the AGC voltage generation circuit 618 e outputs an RF controlsignal Sf1 and IF control signal Sf2 respectively controlling theamplification of the RF amplification circuit 611 and the IFamplification circuit 616.

Next, the operation of the radio wave reception device 61 will bedescribed. FIG. 4 is a flowchart showing the processing of the radiowave reception device 61 of the present embodiment, and FIGS. 5A to 5Eare diagrams showing an outline wave shape of each signal that goesthrough the radio wave reception device 61.

According to FIG. 4, firstly, the low-frequency standard radio wavereceived by the antenna ANT is converted to an electric signal andoutput to the RF amplifier circuit 611. The RF amplifier circuit 611amplifies (attenuates) the input electric signal, in accordance with theRF control signal Sf1 input from the AGC circuit 618, and outputs theamplified (attenuated) signal to the frequency conversion circuit 613via the filter circuit 612.

Next, the frequency conversion circuit 613 converts the input signal toa predetermined intermediate frequency signal and outputs the signal tothe IF amplifier circuit 616 via the filter circuit 615. The IFamplifier circuit 616 amplifies (attenuates) the input signal, inaccordance with the IF control signal Sf2 input from the AGC circuit618, and outputs the amplified (attenuated) signal as the signal Sa, tothe detection circuit 20 via the filter circuit 612 (Step S11). Here, asshown in FIG. 5A, the signal Sa is a signal that has an amplitudemodulation of 10% and 100%.

Then, in the detection circuit 620, the carrier extraction circuit 621outputs the signal Sb that is synchronized with the phase of the carrierof signal Sa. Then, the multiplier 622 a of the signal reproductioncircuit 622 multiplies the signal Sa and signal Sb, and outputs themultiplied signal as signal Sc. The signal Sc is cut off the highfrequency components by the LPF 622 b, and as shown in FIG. 5C, isoutput as the signal Sc′ that is nearly equal to the baseband signal ofsignal Sa (Step S12).

The inverting amplifier 618 a of the AGC circuit 618, inverts andamplifies the signal Sc′, and outputs the signal as signal Sd (StepS13). Then, the multiplier 618 b multiplies the signal Sa and the signalSd, and outputs the multiplied signal as signal Se (Step S14). Namely,as shown in FIG. 5E, the signal Se is output as a signal where the peakmagnitude of the signal Sa is approximately constant.

Next, the AGC detection circuit 618 c detects (for example peak detects)the signal Se, and the detected signal is output to the LPF 618 d. Thehigh-frequency components are cut off, and is output to the AGC voltagegeneration circuit 618 e (Step S15).

The AGC voltage generation circuit 618 c generates and outputs the RFcontrol signal Sf1 for controlling the amplification of the RF amplifiercircuit 611 and IF control signal Sf2 for controlling the amplificationof the IF amplifier circuit 616, in accordance with the signal level ofthe input signal.

In this way, the radio wave reception device 61 multiplies the signal Sathat is an intermediate frequency signal and signal Sd that inverted andamplified the signal Sc′ (more accurately, the signal Sg is a reproducedsignal and the signal Sc′ is approximately equivalent to a reproducedsignal), namely, the radio wave reception device 61 modulates (inversemodulates) the signal Sa at the signal Sc′, and generates the RF controlsignal Sf1 that controls the amplification of the RF amplifier circuit611 and the IF control signal Sf2 that controls the amplification of theIF amplifier circuit 616. In other words, ideally, because the AGCdetection circuit 618 c detects the signal Se that has only theintermediate frequency components, it is not necessary to place a filterhaving a larger time constant than the cycle of the received amplitudemodulation signal to perform the AGC operation, and a high speed AGCoperation, without relying to the cycle of the amplitude modulationsignal is realized.

Second Embodiment

Next, the second embodiment will be described with reference to FIGS. 6to 8E.

The structure of the radio wave clock 1 of the second embodiment, is thesame structure except for the AGC circuit 618 of the radio wavereception device 61 in the first embodiment, being replaced with an AGCcircuit 619 shown in FIG. 6. Therefore, descriptions for the overlappingparts will be omitted by putting the same reference numerals.

FIG. 6 is a block diagram showing an example of a circuit structure ofthe carrier extraction circuit 621, signal reproduction circuit 622, andAGC circuit 619 of the present embodiment. According to FIG. 6, the AGCcircuit 619 comprises an inverting amplifier 619 a, a multiplier 619 b,an adder 619 c, an AGC detection circuit 618 c, an LPF 618 d, and an AGCvoltage generation circuit 618 e.

The signal Sc′ input from the LPF 622 b is input to the invertingamplifier 619 a. Then, the inverting amplifier 619 a inverts andamplifies the signal Sc′ and outputs the inverted and amplified signalSd1.

The signal Sb output from the oscillator 621 c and the signal Sd1 outputfrom the inverting amplifier are input to the multiplier 619 b. Then,the multiplier 619 b multiplies the signal Sb and signal Sd1, andoutputs the multiplied signal Sd2.

The signal Sa output from the filter circuit 617 and the signal Sd2output from the multiplier 619 b, are input to the adder 619 c. Then,the adder 619 c adds the signal Sa and the signal Sd2, and outputs theadded signal Se.

Next, the operation of the radio wave reception device of the presentembodiment will be described. FIG. 7 is a flowchart showing the processof the radio wave reception device 61 of the present embodiment, andFIGS. 8A to 8E are diagrams showing an outline wave shape of each signalthat goes through the radio wave reception device 61. Additionally, onlythe operation of the AGC circuit 619 of the operation of the radio wavereception device 61 of the present embodiment, differs from the abovefirst embodiment. Therefore, in FIG. 7, the same steps as FIG. 4 will beput the same step number as FIG. 4, and will be described focusing onthe different parts.

Namely, when the signal Sc′ is output from the LPF 622 b (Step S11 toS12), the inverting amplifier 619 a of the AGC circuit 619, inverts andamplifies the signal Sc′, and outputs the inverted and amplified signalSd1 (Step S21). As shown in FIG. 8C, the signal Sd1 is a signal thatalmost corresponds to the inverted baseband signal of signal Sa.

Next, the multiplier 619 b multiplies the signal Sb and signal Sd1, andoutputs the multiplied signal Sd2 (Step S22). Sequentially, the adder619 c adds the signal Sa and signal Sd2, and outputs the added signal Se(Step S23). Namely, as shown in FIG. 8E, the signal Se is output as asignal that has a constant signal level, and has the same frequency andsame phase as the signal Sa.

Then, the AGC detection circuit 618 detects the signal Se, and thedetected signal is output to the AGC voltage generation circuit 618 evia the LPF 618 d, and the AGC voltage generation circuit 618 egenerates and outputs the RF control signal Sf1 and IF control signalSf2 (Step S15 to S16).

In this way, the radio wave reception device 61 multiplies the signal Sbthat is the standard signal and the signal Sd1 that inverted andamplified the signal Sc′ that was regenerated by the signal Sd1, namely,the signal Sb is modulated at the signal Sd1, and the modulated signalSd1 is added to the signal Sa that is the intermediate frequency signaland according to the signal level of the added signal Se, the RF controlsignal Sf1 that controls the amplification of the RF amplifier circuit611 and the IF control signal Sf2 that controls the amplification of theIF amplifier circuit, can be generated. Namely, ideally, because the AGCdetection circuit 618 c detects the signal Se that has only theintermediate frequency components, it is not necessary to place a filterhaving a larger time constant than the cycle of the received amplitudemodulation signal to perform the AGC operation, and a high speed AGCoperation, without relying to the cycle of the amplitude modulationsignal is realized.

The first and second embodiment is not limited to the above embodiments,and various embodiments and changes may be made thereunto withoutdeparting from the broad spirit and scope of the invention.

For example, an AGC circuit shown in FIG. 10 may be comprised instead ofthe AGC circuit 618 of FIG. 3 and AGC circuit 619 of FIG. 6. Namely,according to FIG. 10, the AGC circuit 629 comprises a multiplier 629 a,a subtracter 629 b, an AGC detection circuit 618 c, an LPF 618 d, and anAGC voltage generation circuit 618 e.

The signal Sb output from the oscillator 621 c and the signal Sc′ outputfrom the LPF 622 b is input to the multiplier 629 a. Then, themultiplier 629 a multiplies the signal Sb and signal Sc′, and outputs amultiplied signal Sd3.

The signal Sa output from the filter circuit 617 and the signal Sd3output from the multiplier 629 a are input to the subtracter 629 b.Then, the subtracter 629 b subtracts the signal Sd3 from the signal Sa,and outputs the subtracted signal Se.

Here, ideally, the signal Sa and the signal Sd3 have the same waveshape. Therefore, by adequately adjusting the signal level of the signalSd3 (for example, amplifying at a predetermined amplification), in asimilar way as the signal Se shown in FIG. 5E, a signal Se where thepeak amplitude is approximately constant can be gained.

In this case, the radio wave reception device 61 multiples the standardsignal Sb and signal Sc′ that is regenerated by the signal regenerationcircuit 622, namely, the signal Sb is modulated at the signal Sc′, andthe modulated signal Sd3 is added to the signal Sa that is anintermediate frequency signal and according to the signal level of theadded signal Se, generates the RF control signal Sf1 that controls theamplification of the RF amplifier circuit 611 and the IF control signalSf2 that controls the amplification of the IF amplifier circuit 616. Inother words, ideally, because the AGC detection circuit 618 c detectsthe signal Se that has only the intermediate frequency components, it isnot necessary to place a filter having a larger time constant than thecycle of the received amplitude modulation signal to perform the AGCoperation, and a high speed AGC operation, without relying to the cycleof the amplitude modulation signal is realized.

Third Embodiment

FIG. 12 is a block diagram showing a radio wave reception device 1061,replacing the radio wave reception device 61 that comprises the radiowave clock in the first embodiment. According to FIG. 12, the radio wavereception device 1061 is constituted comprising an antenna ANT, RFamplifier circuit 1611, filter circuits 1612, 1615, 1617, frequencyconversion circuit 1613, local oscillation circuit 1614, IF amplifiercircuit 1616, detection circuit 1620, and an AGC (Auto Gain Control)circuit 1618.

The antenna ANT can receive low-frequency standard radio wave, and iscomprised of for example a bar antenna. The received radio wave isconverted to an electric signal and is output.

The signal output from the antenna ANT and an RF control signal Sg1output from the AGC circuit 1618 are input to the RF amplifier circuit1611. The RF amplifier circuit 1611 outputs the signal input from theantenna ANT at amplification (or attenuation) in accordance with the RFcontrol signal Sg1.

The signal output from the RF amplifier circuit 1611 is input to thefilter circuit 1612. The filter circuit 1612 allows signal componentshaving a predetermined range of frequencies to pass through, relating tothe input signal, i.e. outputs the signal, cutting off the frequencycomponents that are out of the range.

The signal output from the RF amplifier circuit 1612 and the signaloutput from the local oscillation circuit 1614 are input to thefrequency conversion circuit 1613. The frequency conversion circuit 1613mixes the two input signals, and outputs the mixed signal as anintermediate frequency signal. The local oscillation circuit 1614generates and outputs the signal of the local oscillation frequencies.

The intermediate frequency signal output from the frequency conversioncircuit 1613 is input to the filter circuit 1615. The filter circuit1615 allows a predetermined range of frequencies, placing theintermediate frequencies in the center, relating to the intermediatefrequency signal and outputs the signal cutting of the frequencycomponents that are out of the range.

The signal output from the filter circuit 1615 and an IF control signalSg2 output from the AGC circuit 1618 are input to the IF amplifiercircuit 1616. The IF amplifier circuit 1616 amplifies (or attenuates)and outputs, in accordance with the amplification of the IF controlsignal Sg2.

The signal output from the IF amplifier circuit 1616 is input to thefilter circuit 1617. Then, the filter circuit 1617 allows signalcomponents having a predetermined range of frequencies, concerning theinput signal to pass through, i.e. outputs the signal as signal Sa,cutting off the frequency components that are out of the range.

The detection circuit 1620 comprises a carrier extraction circuit 1621,a signal mixing circuit 1622, and a signal reproduction circuit 1623.

The carrier extraction circuit 1621 is comprised of for example a PLL(Phase Locked Loop) circuit. The signal Sa output from the filtercircuit 1617 is input to the carrier extraction circuit 1621. Then, asignal Sb that has a signal level that is a constant standard signal andhas the same frequency and the same phase as the signal is output.

The signal Sa output from the filter circuit 1617 and the signal Sboutput from the carrier extraction circuit 1621 are input to the signalmixing circuit 1622. The signal mixing circuit 1622 outputs a signal Sb′that amplified the signal Sb, and a signal Sc that subtracted the signalSb′ from the signal Sa.

The signal Sb output from the carrier extraction circuit 1621 and thesignal Sc output from the signal mixing circuit 1622 are input to thesignal reproduction circuit 1623. The signal reproduction circuit 1623outputs a signal Sf as a baseband signal.

The signal Sb′ and signal Sc output from the signal mixing circuit 1622are input to the AGC circuit 1618. The AGC circuit 1618 outputs the RFcontrol signal Sg1 for controlling the amplification of the RF amplifiercircuit 611 and IF control signal Sg2 for controlling the amplificationof the IF amplifier circuit 1616, in accordance with the intensity(power of the signal level) of the signal Sb′ and Sc. Here, theamplification of the RF amplifier circuit 1611 and the IF amplifiercircuit 1616 is adjusted according to the intensity of the radio wavethat the antenna ANT received. For example, firstly, the AGC circuit1618 controls the intensity of the IF amplifier circuit 1616 by the IFamplifier signal Sg2. However, in a case where the signal level input inthe IF amplifier 1616 is high, and attenuation in the IF amplifiercircuit is not enough, the amplification of the RF amplifier circuit1611 is adjusted by the RF control signal.

FIG. 13 is a block diagram showing an example of a circuit structure ofthe carrier extraction circuit 1621, the signal mixing circuit 1622, thesignal reproduction circuit 1623, and the AGC circuit 1618 in FIG. 12.According to FIG. 13, the carrier extraction circuit 1621 comprises a PD(Phase Detector) 1621 a, an LPF (Low Pass Filter) 1621 b and anoscillator 1621 c.

The signal Sa output from the filter circuit 1617 and the signal outputfrom the oscillator 1621 c are input to the PD 1621 a. The PD 1621 acompares the phase of the two input signals, and outputs aphase-difference signal having a signal level corresponding to thedetected phase difference.

The signal output from the LPF 1621 b is input to the oscillator 1621 b.The LPF 1621 b allows signal components having a predetermined range(low pass) of frequencies, relating to the input to signal, to passthrough, i.e. outputs a signal cutting off the frequency components thatare out of the range.

The signal output from the PD 1621 a is input to the oscillator 1621 c.The oscillator 1621 c adjusts the phase difference of the signal that isto be oscillated, based on the input signal, so that the phase of theoscillated signal synchronizes with the phase of the carrier wave ofsignal Sa, and outputs the adjusted signal as signal Sb.

The signal mixing circuit 1622 comprises an amplifier 1622 a and asubtracter 1622 b. The signal Sb output from the oscillator 1621 c isinput to the amplifier 1622 a. The amplifier 1622 a, as will bedescribed later, amplifies the signal Sb so that the amplitude of signalSc output from the subtracter 1622 b is constant, and outputs the signalas signal Sb′.

The signal Sa output from the filter circuit 1617 and the signal Sb′output from the amplifier 1622 a are input to the subtracter 1622 b. Thesubtracter 1622 b subtracts signal Sb′ from the signal Sa, an outputsthe subtraction result as signal Sc.

The amplification of signal Sb by the amplifier 1622 a that regulatesthe amplification of the signal Sc, output from the subtracter 1622 b,will be described. The low-frequency standard radio wave has anamplitude modulation of 10% and 100%. Therefore, the signal Sa has thesame amplification, and when a maximum amplification of the signal Sa isrepresented as X, the minimum amplification is 0.1X. It is also assumedthat the amplification of signal Sb′ is represented as Y. To make theabsolute value of the amplification of signal Sc constant, wherein thesignal Sc is gained by subtracting signal Sb′ from signal Sa by thesubtracter 622 b, the below relation needs to be:|X−Y|=|0.1X−Y|Y=0.55X

Namely, by setting the amplification of signal Sb′ to 55% of the maximumamplification of signal Sa, the amplification of signal Sc output fromthe subtracter 1622 b, becomes constant.

The signal reproduction circuit 1623 a comprises limiting circuit 1623a, a PD 1623 b, and a LPF 1623 c.

The signal Sc output from the subtracter 1622 b is input to the limitingcircuit 1623 a. The limiting circuit 1623 a limits the amplification ofsignal Sc to a predetermined range of upper limit and lower limit, andoutputs the signal as signal Sd. By the limiting circuit 1623 a, noisethat is included in the signal Sc can be eliminated to a certain extent.

The signal Sb output from the oscillator 1621 c and the signal Sd outputfrom the limiting circuit 1623 a is input to the PD 1623 b. The PD 1623b compares the phase of the signal Sb and Sd, and outputs aphase-difference signal Se having a signal level corresponding to thedetected phase difference. In the present embodiment, if the two signalshave the same phase, the PD 1623 b commutates the wave shape of signalSd to a plus direction, and outputs the signal, and if the two signalshave a negative phase, commutates the wave shape of signal Sd to a minusdirection, and outputs the signal.

The phase difference signal Se output from the PD 1623 b is input to theLPF 1623 c. The LPF 1623 c allows signal components having apredetermined range (low pass) relating to the signal Se to passthrough, i.e. outputs a signal Sf that cuts off frequency componentsthat are out of the range.

The AGC circuit 1618 comprises AGC circuits 1618 a, 1618 c, LPFs 1618 b,1618 d, and a comparator 1618 e.

The signal Sb′ output from the amplifier 1622 a is input to the AGCdetection circuit 1618 a. The AGC detection circuit 1618 a detects thesignal Sb′, and outputs a detected signal.

The signal output from the AGC detection circuit 1618 a is input to theLPF 1618 b. The LPF 1618 b allows a predetermined range (low pass) offrequencies to pass, relating to the input signal, and outputs a signalcutting off the frequency components that are out of the range.

The signal Sc output from the subtracter 1622 b is input to the AGCdetection circuit 1618 c. The detection circuit 1618 c detects thesignal Sc and outputs the detected signal.

The signal output from the AGC detection circuit 1618 c is input to theLPF 1618 d. The LPF 1618 d allows signal components having apredetermined rage (low pass) of frequencies, relating to the inputsignal, to pass through, i.e. outputs a signal, cutting off thefrequency components that are out of the range.

The signal output from the LPF 1618 b and the signal output from the LPF1618 d are input to the comparator 1618 e. The comparator 1618 ecompares the level of the two input signals, and outputs a signal havinga signal level corresponding to a phase-difference of the detected phasedifference.

The signal output from the comparator 1618 e is input to an AGC voltagegeneration circuit 1618 f. The AGC voltage generation circuit 1618 fgenerates and outputs the RF control signal Sg1 and IF control signalSg2 based on the input signal.

Next, the operations of the radio wave reception device 1061 will bedescribed. FIG. 14 is a flowchart showing the processing of the radiowave reception device 1061, and FIGS. 15A to 15F are figures showing theapproximate wave shape of each signal that passes through the radio wavereception device 1061.

According to FIG. 14, firstly, the low-frequency standard radio wavereceived by the antenna ANT is converted to an electric signal, andoutput to the RF amplifier circuit 1611. The RF amplifier circuit 1611amplifies (attenuates) the input signal, in accordance with the RFcontrol signal Sg1 output from the AGC circuit 1618, and outputs theamplified (attenuated) signal to the frequency conversion circuit viathe filter circuit 1612.

Next, the frequency conversion circuit 1613 converts the input signal toa signal of a predetermined intermediate frequency, and outputs theconverted signal to the IF amplifier circuit 1616 via the filter circuit1615. The IF amplifier circuit 1616 amplifies (attenuates) the inputsignal, in accordance with the IF control signal Sg2 input from the AGCcircuit 1618, and outputs the amplified (attenuated) signal as thesignal Sa, to the detection circuit 1620 via the filter circuit 1617(Step S111). Here, as shown in FIG. 15A, the signal Sa is a signal thathas an amplitude modulation of 10% (corresponding to time zone A, C) and100% (corresponding to time zone B).

Then, in the detection circuit 1620, the carrier extraction circuit 1621outputs a signal Sb that has the same frequency and same phase as signalSa, and constant amplitude (Step S112). In the signal mixing circuit1622, the amplifier 1622 a outputs the signal Sb as amplified signalSb′. At this time, the amplifier 1622 a amplifies the signal Sb so thatthe amplification of signal Sb′ becomes 55% of the maximum amplificationof signal Sa (Step S113).

Next, the subtracter 1622 b outputs the signal Sc, which is signal Sb′subtracted from signal Sa. Namely, as shown in FIG. 15C, in time zones Aor B, wherein the modulation of the amplification of signal Sa is 10%,signal Sc has a reversed phase as signal Sb′, and in time zone B,wherein the modulation of the amplification of signal Sa is 100%, signalSc has the same phase as signal Sb′ (Step S114).

Then, in the signal regeneration circuit 1623, the limiting circuit 1623a outputs a signal Sd, cutting off greater or equal to VH and lesser orequal to VL, of the amplification of signal Sc (Step S115). The PD 1623b compares the phase of the signal Sb and Sd, and outputs the signal asSe. Concretely, in a case where the signal Sb and the signal Sd have thesame phase, (time phase A and time phase C), a signal Se, wherein signalSd commutates to a plus direction is output. In a case where the signalSb and the signal Sd have a negative phase, (time phase B), a signal Se,wherein signal Sd commutates to a minus direction is output (Step S116).

Furthermore, the LPF 1623 c allows signal components having apredetermined range (low pass) of frequencies relating to signal Se, topass through, i.e. outputs a signal Sf, cutting off the frequencycomponents that are out of the range (Step S117). Namely, as shown inFIG. 15F, the signal Sf is output as a signal that is nearly equal tothe baseband signal of signal Sa.

In the AGC circuit 1618, the AGC detection circuit 1618 a detects thesignal Sb′, and outputs the detected signal to the comparator 1618 e viathe LPF 1618 d (Step S121). The AGC detection circuit 1618 c detects thesignal Sc, and outputs the detected signal to the comparator 1618 e viathe LPF 1618 d (Step S122).

Then, the comparator 1618 e compares the level of the two input signals,and outputs a signal to the AGC voltage generation circuit 1618 f. TheAGC voltage generation circuit 1618 f generates and outputs an RFcontrol signal Sg1 and an IF control signal Sg2 (Step S123).

The radio wave reception device 1061 detects the signal Sc (the signalafter subtracting signal Sb′, which has the same frequency and phase assignal Sa and a constant amplification, from signal Sa) and the signalSb′, and by comparing the signal levels of the two signals, RF controlsignal Sg1 that controls the amplification of the RF amplifier circuit1611 and IF control signal Sg2 that controls the amplification of the IFamplifier circuit 1616 can be generated. Namely, the AGC detectioncircuit 1618 c detects the signal Sc that has only the intermediatefrequency components. Because of this, the LPF 1618 d needs not to be afilter having a time constant equal to or larger than the cycle of thereceived standard radio wave (amplitude modulation signal). Accordingly,speeding up of the AGC operation of the radio wave reception device 1061can be realized.

Furthermore, the radio wave reception device 1061 converts theamplification modulation of signal Sa to a phase modulation, and bydetermining whether the signal Sd has a same phase or a reversed phaseof signal Sb (namely, a signal synchronized with the phase of thecarrier wave of signal Sa), a signal Sf that corresponds to the basebandsignal of signal Sa is gained. Namely, because detection is carried outplacing the phase of the signal Sa as a standard, a stable detection canbe carried out even when there is a deformation in radio wave shape,such as the amplification of the signal Sa becoming smaller by receivinga weak radio wave.

In the third embodiment, the signal Sb is amplified so that theamplitude of signal Sb′ becomes 55% the maximum amplitude of signal Sa.However, it may be that the amplitude of signal Sb′ is 10% the maximumamplitude of signal Sa. Namely, when a signal that has amplitude of 10%of the maximum amplitude of signal Sa is subtracted from the signal Sa,there is a signal at a modulation of 100%, but at a modulation of 10%,the signal is erased. Therefore, by determining whether there is asignal or not based on the subtraction result by the subtracter 1622 b,it is possible to detect the signal Sa.

The third embodiment is not limited to the above embodiment, and variousembodiments and changes may be made thereunto without departing from thebroad spirit and scope of the invention.

For example, in the AGC circuit 1618, the signal Sb′ and signal Sc aredetected, and after the high frequency wave components are cut off, thetwo signals are compared. However, the signal level of signal Sc may becompared to a predetermined signal level, and the RF control signal Sg1and IF control signal Sg2 may be generated in accordance with thecomparison result.

Fourth Embodiment

FIG. 16 is a block diagram showing a radio wave reception device 2061,employing a super heterodyne type, replacing the radio wave receptiondevice 61 that comprises the radio wave clock 1 in the first embodiment.According to FIG. 16, the radio wave reception device 2061 isconstituted comprising an antenna 2001, RF amplifier circuit 2002,filter circuits 2003, 2006, 2008, frequency conversion circuit 2004,local oscillation circuit 2005, IF amplifier circuit 2007, detectioncircuit 2009, and an AGC circuit 2010.

The antenna 2001 can receive low-frequency standard radio wave, and isconstituted by, for example, a bar antenna. A received radio wave isconverted into an electric signal and then output as signal Sa. Thesignal Sa and RF control signal Se1 output from the AGC circuit 2010 isinput to the RF amplifier circuit 2002. The RF amplifier circuit 2002amplifies and outputs the signal Sa, which was input according to the RFcontrol signal Se1.

The signal output from the RF amplifier circuit 2002 is input to thefilter circuit 2003. Signal components having a predetermined range offrequencies, relating to the input signal, are allowed to pass through,and the frequency components that are out of the range are cut off. Asignal of local oscillation frequencies is generated in the localoscillation circuit 2005. The signal output from the signal filtercircuit 2003 and the signal output from the local oscillation circuit2005 are input to the frequency conversion circuit 2004. The two signalsare mixed, and output as an intermediate frequency signal.

The intermediate frequency signal output from the frequency conversioncircuit 2004 is input to the filter circuit 2006. The filter circuit2006 allows signal components having a predetermined range offrequencies to pass through, where the intermediate frequency of theintermediate frequency signal is placed in the center, i.e. outputs asignal, cutting off frequency components that are out of the range.

The signal output from the filter circuit 2006 and an IF control signalSe2 output from the AGC circuit 2010 are input to the IF amplifiercircuit 2007. The IF amplifier circuit 2007 amplifies and outputs theinput signal, in accordance with the IF control signal Se2. The signaloutput from the IF amplifier circuit is input to the filter circuit2008. Then, signal components having a predetermined range offrequencies are allowed to pass through, i.e. signal Sb is output,cutting off the frequency components that are out of the range.

The detection circuit 2009 comprises a carrier extraction circuit 2091and a signal reproduction circuit 2092. The carrier extraction circuit2091 is comprised of for example a PLL (Phase Locked Loop) circuit. Thesignal Sb, output from the filter circuit 2008, is input to the carrierextraction circuit 2091. Then, a signal that is synchronized with thecarrier wave of signal Sb, is output.

The signal Sb output from the filter circuit 2008, the signal Sc outputfrom the carrier extraction circuit 2091, and the signal Se3 output fromthe AGC circuit 2010 are input to the signal reproduction circuit 2092.Then, the signal Sd and detection signal Sf are output based on thesethree signals.

The signal Sd output from the signal reproduction circuit 2092 is inputto the AGC circuit 2010. Then, RF amplifier signal Se1, IF amplifiersignals Se2 and Se3 are output as gain control signals. Concretely, thesignal Sd and standard voltage are compared, and signal Se3 is output aphase-difference signal having a signal level corresponding to thedetected phase difference. Based on the signal Se3, RF amplifier signalSe1 and IF amplifier signal Se2 are output.

FIG. 17 is a circuit block diagram showing the structure of the carrierextraction circuit 2091, signal reproduction circuit 2092, and AGCcircuit 2010 in FIG. 16. The carrier extraction circuit 2091 comprises aPD (Phase Detector) 9101, an LPF (Low Pass Filter) 9102, and anoscillator 9103.

The signal Sb output from the filter circuit 2008 and the signal outputfrom the oscillator 9103 are input to the PD 9101. The two signals arecompared by the PD 9101, and outputs a phase-difference signal having asignal level corresponding to the detected phase difference. The signaloutput from the PD 9101 is input to the LPF 9102. The signal componentshaving a predetermined range (low pass) of frequencies is allowed topass through, i.e. a signal is output, cutting off frequency componentsthat are out of the range.

The signal output from the LPF 9102 is input to the oscillator 9103. Theoscillator 9103 adjusts the phase of the signal to be oscillated, basedon the signal output from the LPF 9102, so that the signal to beoscillated is synchronized with the phase of carrier wave of signal Sb.The signal Sc that is synchronized with the phase of the carrier wave ofsignal Sb is output from the oscillator 9103.

The signal reproduction circuit 2092 comprises multiplication circuits9201, 9203, and LPFs 9202 and 9204. The signal Sb output from the filtercircuit 2008 and signal Sc output from the oscillator 9103 are input tothe multiplication circuit 9201. The two signals are output after beingmultiplied.

The signal output from the multiplier circuit 9201 is input to the LPF9202. A predetermined range (low pass) relating to the signal is allowedto pass through, and cutting off the frequency components that are outof the range, the signal Sd is output. The signal Sd output from the LPF9202 and the signal Se3 output from the AGC circuit 2010 are input tothe multiplication circuit 9203. The two signals are output multiplied.The signal output from the multiplication circuit 9203 is input to theLPF 9204. Then, signal components having a predetermined range (lowpass) relating to the signal is allowed to pass through, i.e. thedetection signal Sf is output, cutting of the frequency components thatare out of the range.

The AGC circuit 2010 comprises a comparison circuit 2101, a standardpower source 2102 and an AGC voltage generation circuit 2103. The signalSd output from the LPF 9202 and a standard voltage supplied by thestandard power source 2102 are input to the comparison circuit 2101.Then, the signal level of signal Sd and the standard voltage arecompared, and outputs a phase-difference signal Se3 having a signallevel corresponding to the detected phase difference.

The signal Se3 is input to the AGC voltage generation circuit 2103, andbased on the signal Se3, RF control signal Se1 and IF control signal Se2is output. The amplification of the RF amplification circuit 2002 and IFamplification circuit 2007 are adjusted based on the intensity of theradio wave that the antenna 2001 receives. For example, theamplification of the IF amplification circuit 2007 is adjusted by the IFcontrol signal Se2. However, in a case where the level of the signalinput to the IF amplification circuit is high, and the attenuation inthe IF amplification circuit 2007 is not enough, the amplification ofthe RF amplification circuit 2002 is also adjusted by the RF controlsignal Se1.

FIGS. 18A to 18E are drawings showing the outline wave shape of eachsignal that passes through the radio wave reception device 2061. Below,the circuit operation of the radio wave reception device 2061 will bedescribed with reference to FIGS. 18A to 18E.

Firstly, a signal Sa is received by the antenna 2001. The signal Sa isamplified by the RF amplification circuit 2002. Here, the signal Sainput to the RF amplification circuit 2002, in accordance with the RFcontrol signal Se1 output from the AGC voltage generation circuit 2103,is amplified (or attenuated).

The signal output from the RF amplification circuit 2002 is input to theIF amplification circuit 2007 via the frequency conversion circuit 2004and filter circuit 2006, and amplified. Here, the signal input to the IFamplification circuit 2007, in accordance with the IF control signal Se2output from the AGC voltage generation circuit 2103, is amplified (orattenuated).

The signal output from the IF amplification circuit 2007 is input to thefilter circuit 2008. Then, the filter circuit 2008 outputs a signal Sb.As shown in FIGS. 18A and 18B, the signal Sa received by the antenna2001, is converted to the signal Sb that has a small amplitudemodulation, by the RF amplification circuit 2002 and IF amplificationcircuit 2007. Namely, the RF amplification circuit 2002 and IFamplification circuit 2007 amplifies (attenuates) so that the level ofthe input signal is retained at a predetermined level, and output.

A transitional amplitude fluctuation occurs at the point where theamplitude changes, to the signal Se3 output from the comparison circuit2101, by the delay of the loop circuit comprised of the RF amplificationcircuit 2002, filter circuit 2003, frequency conversion circuit 2004,filter circuit 2006, IF amplification circuit 2007, and AGC circuit 2010and the LPF 9202. The RF control signal e1 and If control signal e2 aregenerated based on the signal Se3, and the signal b that was adjustedthe amplification by the RF amplification circuit 2 and the IFamplification circuit 7 is converged to a steady value.

The signal Sb and signal Sc are multiplied by the multiplication circuit9201. Because the signal Sc is a signal that is synchronized with thecarrier wave of signal Sb, a modulation component, and a frequencycomponent that is twice the carrier wave is made.

The signal output from the multiplication circuit 9201 takes out onlythe frequency components that are input to the LPF 9202, and is outputas signal Sd. As shown in FIG. 4, by the delay of the time constant ofthe LPF 9202, the signal Sd becomes a signal that oscillates, rises andfalls, at the point where the amplification of the signal output fromthe multiplication circuit 9201 (direct current of signal Sb) changes.

In the LPF 9202, a harmonic component included in the signal output fromthe multiplication circuit 9201 is reduced. Concretely, for example, asignal of twice the frequency of the carrier wave of signal Sb isreduced. If the intermediate frequency is 50 [kHz], the LPF 9202 is asignal that eliminates a signal of 100 [kHz]. Namely, compared with thecycle of the modulation signal of the low-frequency standard radio wave,because the time constant of the LPF 9202 becomes quite small, delay bythe time constant can be reduced. Namely, a high-speed AGC operation canbe realized.

Sequentially, the signal Sd is input to the comparison circuit 2101. Thesignal level of signal Sd and the standard voltage output from thestandard power source 2102, and a signal Se3 is output.

The signal Sd and signal Se3 are input to the multiplication circuit9203. The signal output from the multiplication circuit 9203 is outputas a detection signal Sf10. By inputting the signal Sd and signal Se3 tothe multiplication circuit 9203, the detection signal Sf10 can beadequately reproduced. Then, the detection signal Sf10 is input to atime code generation unit 2910.

As the above, by the RF amplification circuit 2002 and IF amplificationcircuit 2007 that amplifies the input signal according to the RF controlsignal e1 and If control signal e2 output from the AGC circuit 2010, theamplitude fluctuation of the amplitude modulation signal that wasreceived in the antenna 2001, can be retained at a situation close to acertain level. Therefore, it is not necessary to place a filter having alarger time constant than the cycle of the amplitude modulation signalto perform the AGC operation. Namely, a high speed AGC operation isoperated without relying to the cycle of the amplitude modulationsignal.

Therefore, fluctuation of the received radio wave, by transferring,etc., the radio wave clock, can be responded to at once, and timecorrection by the internal circuit of the radio wave clock can beprecisely conducted.

Fifth Embodiment

In the fourth embodiment, the radio wave reception device that appliesthe multiplication circuit 9203, and comprises the signal reproductioncircuit 2092 is described. In this embodiment, as shown in FIG. 19, aradio wave reception device that applies an addition circuit 9301, andcomprises a signal reproduction circuit 2093 will be described.

The structure of the radio wave clock in the fifth embodiment, is thesame as the radio wave clock 1 in FIG. 1. The structure of the radiowave reception device is the same structure replacing the signalreproduction circuit 2092 of the detection circuit 2009 that comprisesthe radio wave reception device 2061 of FIG. 16 to a signal reproductioncircuit 2093 of a detection circuit 2009 a shown in FIG. 19.Furthermore, the structure of the AGC circuit 2010 of FIG. 19 has thesame structure as the AGC circuit 2010 of FIG. 16. Therefore,descriptions for the overlapping parts will be omitted by putting thesame reference numerals.

In the signal reproduction circuit 2093, the signal Sb output from thefilter circuit 2008 and the signal Sc output from the carrier extractioncircuit 2091 are input to the multiplication circuit 9201. The signaloutput from the multiplication circuit 9201 is input to the LPF 9202.

The signal Sd output from the LPF 9202 and the signal Se3 output fromthe comparison circuit 2101 are input to the addition circuit 9301. Thetwo signals are added by the addition circuit 9301, and a detectionsignal Sf20 is output via the LPF 9204. The detection signal Sf20 hasalmost the same wave shape as detection signal Sf10, and becomes a waveshape that is biased a predetermined level by the direct currentcomponent.

The detection signal Sf20 is input to the time code generation unit2910. The time code generation unit 2910 generates a standard time codebased on the pulse width from the rising edge to the falling edge of thedetection signal Sf20. Therefore, there is no problem that the signallevel of the detection signal Sf20 is biased a predetermined level,compared to the detection signal Sf10.

By the above, the fifth embodiment has the same effects as the fourthembodiment. Namely, by the RF amplification circuit 2002 and IFamplification circuit 2007 that amplifies (attenuates) the input signalaccording to the RF control signal Se1 and IF control signal Se2 outputfrom the AGC circuit 2010, the amplitude fluctuation of the amplitudemodulation signal that was received in the antenna 2001, can be retainedat a situation close to a certain level. Therefore, it is not necessaryto place a filter having a larger time constant than the cycle of theamplitude modulation signal to perform the AGC operation. Namely, a highspeed AGC operation is operated without relying to the cycle of theamplitude modulation signal.

Therefore, fluctuation of the received radio wave, by transferring,etc., the radio wave clock, can be responded to at once, and timecorrection by the internal circuit of the radio wave clock can beprecisely conducted.

Sixth Embodiment

In the fifth embodiment, the radio wave reception device that appliesthe addition circuit 9301 and comprises the signal reproduction circuit2093 is described. In the present embodiment, as shown in FIG. 20, aradio wave reception device that applies a selection circuit 9401 andcomprises a signal reproduction circuit 2094 will be described.

The structure of the radio wave clock in the sixth embodiment, is thesame as the radio wave clock 1 in FIG. 1. The structure of the radiowave reception device is the same structure replacing the signalreproduction circuit 2092 of the detection circuit 2009 that comprisesthe radio wave reception device 2061 of FIG. 16 to a signal reproductioncircuit 2094 of a detection circuit 2009 b shown in FIG. 20. Therefore,descriptions for the overlapping parts will be omitted by putting thesame reference numerals.

In the signal reproduction circuit 2094, the signal Sb output from thefilter circuit 2008, and the signal Sc output from the carrierextraction circuit 2091, are input to the multiplication circuit 9201.The signal output from the multiplication circuit 9201 is input to theLPF 9202.

The signal Sd output from the LPF 9202 and the signal Se3 output fromthe comparison circuit 2101 are input to the selection circuit 9401. Theselection circuit 9401 selects either the signal Sd or Se3, and outputsthe signal as detection circuit Sf30 via the LPF 9204.

Concretely, in a case where the amplification of the RF amplificationcircuit 2002 and IF amplification circuit 2007, which are determinedaccording to the RF control signal Se1 and If control Se2, are in apredetermined range, and the amplitude fluctuation of the signal Sd issmall, (Signal Sd of FIG. 18C), signal Se3 is selected by the selectioncircuit 9401. On the other hand, in a case where the amplification ofthe RF amplification circuit 2002 and the IF amplification circuit 2007are not in a predetermined range, and the signal Sd fluctuates to acertain extent, being synchronized with the amplitude fluctuation ofsignal Sa.

As the above, by the RF amplification circuit 2002 and IF amplificationcircuit 2007 that amplifies the input signal according to the RF controlsignal Se1 and IF control signal Se2 output from the AGC circuit 2010,the amplitude fluctuation of the amplitude modulation signal that wasreceived in the antenna 2001, can be retained at a situation close to acertain level. Therefore, it is not necessary to place a filter having alarger time constant than the cycle of the amplitude modulation signalto perform the AGC operation. Namely, a high speed AGC operation isoperated without relying to the cycle of the amplitude modulationsignal.

Therefore, fluctuation of the received radio wave, by transferring,etc., the radio wave clock, can be responded to at once, and timecorrection by the internal circuit of the radio wave clock can beprecisely conducted.

Seventh Embodiment

The seventh embodiment will be described with reference to FIG. 9.

In the above first to sixth embodiment, a radio wave clock applying thepresent invention is described. In the present embodiment, a repeaterwill be described. A repeater is for example placed at the window ofsteel framed house, etc., where it is difficult to receive radio wavesin the interior. The repeater receives a low-frequency standard radiowave and obtains correct time information, and sends this timeinformation to the radio wave clock. The radio wave clock that is placedindoors, etc., receives the time information sent from the repeater, andconducts time correction.

FIG. 9 is a block diagram showing an example of a circuit structure of arepeater 2 applied in the present invention. The structure of therepeater 2 is the same structure as the radio wave clock 1 in FIG. 1,except that a sending unit is added. Therefore, descriptions for theoverlapping parts will be omitted by putting the same referencenumerals.

The sending unit 90 sends the standard time code input from the CPU 10,by a predetermined carrier wave, as an intermediate radio wave, by anantenna, etc. The carrier wave may be the same as the low-frequencystandard radio wave that is to be received, or a dedicated radio wave asan intermediate radio wave. In a case where the carrier wave is the sameas the low-frequency standard radio wave, the radio wave clock placeindoors, etc., may be an ordinary radio wave clock. In a case where thecarrier wave is a dedicated radio wave as an intermediate radio wave, itis necessary for the radio wave clock to comprise a means for receivingthe radio wave.

As the above, by the Rf amplification circuit 2002 and IF amplificationcircuit 2007 that amplifies the input signal according to the RF controlsignal Se1 and If control signal Se2 output from the AGC circuit 2010,the amplitude fluctuation of the amplitude modulation signal that wasreceived in the antenna 2001, can be retained at a situation close to acertain level. Therefore, it is not necessary to place a filter having alarger time constant than the cycle of the amplitude modulation signalto perform the AGC operation. Namely, a high speed AGC operation isoperated without relying to the cycle of the amplitude modulationsignal.

Therefore, even in a case where a repeater receives a standard radiowave signal, where the signal level fluctuates by obstacles, or weather,etc., AGC operation can be speedily performed. As a result, timecorrection by the internal circuit of the repeater can be preciselyconducted. Furthermore, it is not necessary to design a circuit takinginto consideration, the delay by the AGC operation, and complexity ofradio reception devices can be prevented.

The first and second embodiment is not limited to the above embodiments,and various embodiments and changes may be made thereunto withoutdeparting from the broad spirit and scope of the invention.

For example, the radio wave reception device 2061 comprises an RFamplification circuit 2002 and IF amplification circuit 2007. However,the radio wave reception device 2061 may comprise either the RFamplification circuit 2002 or the IF amplification circuit 2007. Namely,the radio wave reception device may be a device such as the radio wavereception device 2971A, shown in FIG. 21. The radio wave receptiondevice 2971A comprises an RF amplification circuit 2002, and does notcomprise an IF amplification circuit 2007. The radio wave receptiondevice may be a device such as the radio wave reception device 2971B,shown in FIG. 22. The radio wave reception device 2971B does notcomprise an RF amplification circuit 2002, but comprises an IFamplification circuit 2007. The same effects as above are obtained byreplacing the radio wave reception device 2061 that the radio wave clock1 and the repeater 2 comprises, to the radio wave reception device 2971Aor 2971B.

The LPFs 9204 in the signal reproduction circuits 2092, 2093, and 2094may be placed where code L is located.

Eighth Embodiment

FIG. 23 is a block diagram showing a radio wave reception device 3917,employing a super heterodyne type, replacing the radio wave receptiondevice 61 that comprises the radio wave clock 1 in the first embodiment.According to FIG. 23, the radio wave reception device 3917 isconstituted comprising an antenna 3001, RF amplifier circuit 3002,filter circuits 3003, 3006, 3008, frequency conversion circuit 3004,local oscillation circuit 3005, IF amplifier circuit 3007, carrierextraction circuit 3009, signal reproduction circuit 3010, and an AGCcircuit 3011.

The antenna 3001 can receive long wave standard waves, and is comprisedof for example, a bar antenna, etc. The received radio wave is output,converted to an electric signal. The RF amplification circuit 3002amplifies and outputs the signal input from the antenna 3001.

The filter circuit 3003 allows a predetermined range of frequenciesrelating to the signal input from the RF amplification circuit 3002, andoutputs the signal, cutting off the frequency components that are out ofthe range. The frequency conversion circuit 3004 mixes the signal inputfrom the filter circuit 3003 and the signal input from the localoscillation circuit 3005, and outputs the signal converting the signalto a signal of intermediate frequency. The local oscillator 3005generates a signal of local oscillation frequency, and outputs thesignal to the frequency conversion circuit 3004.

The filter circuit 3006 allows signal components having frequencies of apredetermined range to pass through, relating to the signal input fromthe frequency conversion circuit 3004, and cuts off frequency componentsthat are out of the range. The IF amplification circuit 3007 amplifiesand outputs the signal input from the filter circuit 3006. The filtercircuit 3008 allows signal components having frequencies of apredetermined range to pass through, relating to the signal input fromthe IF amplification circuit 3007, i.e. outputs the signal as Sa,cutting off frequency components that are out of the range.

The carrier extraction circuit 3009 is comprised by for example a PLL(Phase Locked Loop) etc., and outputs the signal Sb that has the samefrequency and same phase as the carrier (carrier wave). The signalreproduction circuit 3010 inputs the signals Sa and Sb from the filtercircuit 3008 and carrier extraction circuit 3009, and outputs thesignals as a baseband signal Sf. The AGC circuit 3011 outputs thecontrol signal that adjusts the amplification of the RF amplificationcircuit 3002 IF amplification circuit 3007, according to the intensityof the signal Sa input from the filter circuit 3008.

FIG. 24 is a block diagram showing the structure of the carrierextraction circuit 3009 and signal reproduction circuit 3010. Thecarrier extraction circuit 3009 comprises a PD (Phase Detector) 3091, anLPF (Low Pass Filter) 3092, and an oscillator 3093.

The PD 3091 compares the phase of the signal Sa input from the filtercircuit 3008, and the phase of the signal input from the oscillator3093, and outputs a phase-difference signal having a signal levelcorresponding to the detected phase difference. The PD inputs a signalbased on the phase comparison result to the LPF 3092, and the LPF 3092allows signal components having frequencies of a predetermined range(low pass), relating to the signal, to pass through, i.e. outputs asignal, cutting off the frequency components that are out of the range.The oscillator 3093 adjusts the signal that is to be oscillated based onthe signal output from the LPF 3092, to output a signal that is inaccordance with the phase difference of the carrier wave of signal Sa,and outputs the adjusted signal as signal Sb.

The signal reproduction circuit 3010 comprises a level detection circuit3101, an amplifier 3102, a subtracter 3103, a limiting circuit 3104, aPD 3105 and an LPF 3106, etc. The level detection circuit 3101 detectsfor example, the maximum amplitude of signal Sa, and outputs a signalbased on the detection result to the amplifier 3102. The amplifier 3102amplifies the signal Sb input from the oscillator 3093 based on thesignal input from the level detection circuit 3101 so that the amplitudeof the signal Sc output from the subtracter 3103, which will bedescribed later, is constant, and outputs the signal as signal Sb′.

The subtracter 3103 inputs the signal Sa from the filter circuit 3008,and the signal Sb′ from the amplifier 3102, and outputs the signal Sc,subtracting the signal Sb′ from the signal Sa. The limiting circuit 3104limits the amplification of signal Sc to a predetermined range of upperlimit and lower limit, and outputs the signal as signal Sd. By thelimiting circuit 3104, noise that is included in the signal Sc can beeliminated to a certain extent.

The PD 3105 compares the phase of the signal Sb input from theoscillator 3193, and the phase of the signal Sd input from the limitingcircuit 3104, and outputs a phase-difference signal Se having a signallevel corresponding to the detected phase difference. In the presentembodiment, in a case where the phase of the signal Sb input from theoscillator 3193 has the same phase as the phase of signal Sd, the PD3105 commutates the wave shape of signal Sd to a plus direction, andoutputs the signal, and in a case where the two signals have a negativephase, commutates the wave shape of signal Sd to a minus direction, andoutputs the signal. The signal Se is input from the PD 3105 to the LPF3106, and the LPF 3106 allows signal components having frequencies of apredetermined range (low pass), relating to the signal, to pass through,i.e. outputs a signal cutting off the frequency components that are outof the range.

The amplification of signal Sb′ that regulates the amplification of thesignal Sc, output from the subtracter 3103, will be described. Thelow-frequency standard radio wave has an amplitude modulation of 10% and100%. Therefore, the signal Sa has the same amplification, and when amaximum amplification of the signal Sa is represented as X, the minimumamplification is 0.1X. It is also assumed that the amplification ofsignal Sb′ is represented as Y. To make the absolute value of theamplification of signal Sc constant, wherein the signal Sc is gained bysubtracting signal Sb′ from signal Sa by the subtracter 3103, the belowrelation needs to be:|X−Y|=|0.1X−Y|Y=0.55X

Namely, by setting the amplification of signal Sb′ to 55% of the maximumamplification of signal Sa, the amplification of signal Sc output fromthe subtracter 3103 becomes constant.

FIGS. 25A to 25F are diagrams showing the wave shape of each signal thatgoes through the signal reproduction circuit 3010. FIG. 26 is aflowchart showing the flow of processing of the signal reproductioncircuit 3010. Below, the circuit operations of the signal reproductioncircuit 3010 will be described.

First, the subtracter subtracts signal Sb′ from signal Sa, and outputssignal Sc (Step S301). Here, the amplitude of signal Sa is detected bythe level detection circuit 3101, and the amplifier 3102 amplifies thesignal Sb based on the detection result, and outputs a signal Sb′. Atthis time, signal Sb′ is amplified so that the amplitude of the signalSb′ is 55% of the maximum amplitude of signal Sa. By subtracting signalSb′ from signal Sa, in time zones A and C, where the modulation ofamplitude of signal Sa is 10%, signal Sc has a reversed phase as signalSb′, and in a time zone B, where the modulation of amplitude of signalSa is 100%, signal Sc has the same phase as signal Sb′.

Next, the limiting circuit 3104 cuts off amplitudes of signal Sc thatare greater or equal to VH and smaller or equal to VL, and outputs asignal Sd (Step S302). The PD 3105 compares the phases of the signal Sband signal Sd and outputs a signal Se (Step S303). Because signal Sb hasthe same phase as signal Sb′, the wave shape of signal Sb will not beshown. In a case where signal Sb has the same phase as signal Sd (time Aand C), the PD 3105 commutates signal Sb to a plus direction. In a casewhere the signal Sb has a revered phase of signal Sd, the signal Sd iscommutated to a minus direction.

The LPF 3106 allows signal components relating to signal Se, havingfrequencies of a predetermined low frequency range (low pass) to passthrough, i.e. outputs a signal SF, cutting off the frequency componentsthat are out of the range.

In this way, the amplification modulation of signal Sa is converted to aphase modulation, and by determining whether that signal has the samephase or a reversed phase of signal Sb, a signal Sf that corresponds tothe baseband signal of signal Sa can be gained. Therefore, even in acase where the wave shape changes, such as the amplitude of signal Sabecoming smaller, by receiving weak radio waves, because a detection iscarried out placing the phase of the signal Sa as a standard, a stabledetection can be carried out even when a weak radio wave is received.

Because the noise of signal Sc is eliminated by the limiting circuit3104, a filter circuit that has an extremely narrow band, does not haveto be applied. Therefore, delay occurrence by the filter circuit can beprevented.

In the present embodiment, it is described that the amplitude of signalSb′ is 55% the maximum amplitude of signal Sa. However, the maximumamplitude of signal Sa may be 10%. Namely, when a signal that hasamplitude that is 10% of the maximum amplitude of signal Sa, issubtracted from signal Sa, there is a signal at a modulation of 100%,but a signal at a modulation of 10% is erased. Therefore, by determiningwhether there is a signal or not by the subtraction result, it ispossible to detect signal Sa.

Ninth Embodiment

In the first embodiment, the radio wave reception device included in theradio wave clock was described. In the present embodiment, a repeaterwill be described. A repeater is for example placed at the window ofsteel framed house, etc., where it is difficult to receive radio wavesin the interior. The repeater receives a low-frequency standard radiowave and obtains correct time information, and sends this timeinformation to the radio wave clock. The radio wave clock that is placedindoors, etc., receives the time information sent from the repeater, andconducts time correction.

FIG. 9 is a circuit structure of the repeater 2. The structure of therepeater in the present embodiment, is the same as the structure of theradio wave clock 1 of FIG. 1, except that a sending unit 90 is added.The structure of the radio wave reception device is the same as theradio wave reception device 3917 of FIG. 23.

The sending unit 90 sends the standard time code input from the CPU 10,by a predetermined carrier wave, as an intermediate radio wave, by anantenna, etc. The carrier wave may be the same as the low-frequencystandard radio wave that is to be received, or a dedicated radio wave asan intermediate radio wave. In a case where the carrier wave is the sameas the low-frequency standard radio wave, the radio wave clock placedindoors, etc., may be an ordinary radio wave clock. In a case where thecarrier wave is a dedicated radio wave as an intermediate radio wave, itis necessary for the radio wave clock to comprise a means for receivingthe radio wave.

By the above, because the repeater converts the amplitude modulation ofthe intermediate frequency signals to phase modulation, and detects bysetting the phase as the standard, even when the wave shape of theintermediate frequency signals are changed by receiving weak radiowaves, the standard time code can be detected, and stable repeater radiowaves can be received at all times.

The eighth and ninth embodiments are not limited to the aboveembodiment, and various embodiments and changes may be made thereuntowithout departing from the broad spirit and scope of the invention.

Tenth Embodiment

FIG. 27 is a block diagram showing a radio wave reception device 4917,employing a super heterodyne type, replacing the radio wave receptiondevice 61 that comprises the radio wave clock 1 in the first embodiment.According to FIG. 27, the radio wave reception device 4917 isconstituted comprising an antenna 4001, RF amplifier circuit 4002,filter circuits 4003, 4006, 4008, frequency conversion circuit 4004,local oscillation circuit 4005, IF amplifier circuit 4007, carrierextraction circuit 4009, signal reproduction circuit 4010, and an AGC(Auto Gain Control) circuit 4011.

The antenna 4001 can receive low-frequency standard radio wave, and isconstituted by, for example, a bar antenna. A received radio wave isconverted into an electric signal and then output. The RF amplifiercircuit 4002 amplifies and outputs the signal input from the antenna4001.

The filter circuit 4003 allows a predetermined range of signalcomponents relating to the signal input from the RF amplifier circuit4002 to pass through, i.e. outputs the signal, cutting off the frequencycomponents that are out of the range. The frequency conversion circuit4004 mixes the signal input from the filter circuit 4003 to the signalinput from the local oscillation circuit 4005, and outputs the mixedsignal, converting the signal to a signal of intermediate frequency. Thelocal oscillation circuit 4005 generates a signal of local oscillationfrequency, and outputs the signal to the frequency conversion circuit4004.

The filter circuit 4006 allows signal components relating to the signalinput from the RF amplification circuit 4002, having frequencies of apredetermined range to pass through, where the intermediate frequency ofthe intermediate frequency signal is placed in the center, i.e., thefilter circuit 4006 outputs the signal cutting off the frequencycomponents that are out of the range. The filter circuit 4008 allowssignal components relating to the signal input from the IF amplificationcircuit 4007, having frequencies of a predetermined range to passthrough, i.e. outputs a signal Sp, cutting off the frequency componentsthat are out of the range.

The carrier extraction circuit 4009 is comprised by for example a PLL(Phase Locked Loop) etc., and outputs the signal Sq that has the samefrequency and same phase as the carrier (carrier wave). The signalreproduction circuit 4010 inputs the signals Sp and Sq from the filtercircuit 4008 and carrier extraction circuit 4009, and outputs thesignals as a baseband signal Sr. The AGC circuit 4011 outputs thecontrol signal that adjusts the amplification of the RF amplificationcircuit 4002 IF amplification circuit 4007, according to the intensityof the signal Sp input from the filter circuit 4008.

FIG. 28 is a circuit block diagram showing the structure of the signalreproduction circuit 4010. The signal reproduction circuit 4010comprises multiplication circuits 4010C, 4010D, phase shifters 4103,4106, and an adder 4107.

The multiplication circuit 4020C includes a multiplier 4101, and an LPF(Low Pass Filter) 4102. The multiplier 4101 multiplies the signal Spinput from the filter circuit 4008 and the signal Sq input from thecarrier extraction circuit 4008, and outputs a signal Sd1. The LPF 4102allows a predetermined range of frequency components relating to thesignal Sd1 input from the multiplier 4101, i.e. outputs a signal Se1,cutting off the frequency components that are out of the range.

The phase shifter 4103 delays the phase 90 degrees of the signal Sc1input from the LPF 4105, and outputs the signal as Sa1. Themultiplication circuit 4010D includes a multiplier 4104 and an LPF 4105.The multiplier 4104 multiplies the signal Sa1 input from the phaseshifter 4103 and the signal Sq input from the carrier extraction signal4009, and outputs the signal Sb1. The LPF 4105 allows a predeterminedrange (low pass) of frequency components relating to the signal Sb1input from the multiplier 4104, i.e. outputs a signal Sc1, cutting offthe frequency components that are out of the range.

The phase shifter 4106 delays the phase of the signal Sc1 input from theLPF 4105, and outputs the signal as Sf1. The adder 4107 adds the signalSe1 output from the LPF 4102 and the signal Sf1 output from the phaseshifter 4106, and outputs a signal Sr.

Next, each signal will be described. The signal Sp output from thefilter circuit 4008 includes a desired reception signal (a signal thathas the desired frequency to be received), and noise. The frequency ofthe desired reception signal is assumed to be ω, and the signal wavethereof A sin ωt. Here, amplitude A is a time function. However, theamplitude A changes at a long cycle (1/few seconds), at a low-frequencystandard radio wave. Furthermore, because the modulation of amplitude Ais 10% or 100%, the amplitude A is approximately a constant number.Therefore, as shown in expression (1), the signal Sp can be expressed bymixing the amplitude component A of the designated reception signal andnoise amplitude component B.

[Expression 1]Sp=A sin ωt+B[sin {(ω+Δω)t+φ}+cos {(ω+Δω)t+φ}]  (1)

The phase shifter 4103 inputs the signal Sp, and outputs a signal Sa1,delaying the phase of the signal 90 degrees. Therefore:

[Expression 2]Sa1=A cos ωt+B[−cos {(ω+Δω)t+φ}+sin {(ω+Δω)t+φ}]  (2)

Because the signal Sq output from a carrier extraction signal 4009 issin ωt, the signal Sb1 output from the multiplier 4104 is:

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack & \; \\\begin{matrix}{{{Sa}\; 1} = {{{- A}\;\cos\;\omega\; t} + {{B\begin{bmatrix}{{{- \cos}\left\{ {{\left( {\omega + {\Delta\omega}} \right)t} + \phi} \right\}} +} \\{\sin\left\{ {{\left( {\omega + {\Delta\omega}} \right)t} + \phi} \right\}}\end{bmatrix}}\sin\;\omega\; t}}} \\{= {{{- \left( {A/2} \right)}\sin\; 2\omega\; t} + {B\begin{bmatrix}{{{- \cos}\;\omega\;{t \cdot \left( {{{\Delta\omega}\; t} + \phi} \right)}} + {\sin\;\omega\;{t \cdot}}} \\{{\sin\left( {{{\Delta\omega}\; t} + \phi} \right)} + {\sin\;\omega\;{t \cdot \cos}}} \\{\left( {{\Delta\;\omega\; t} + \phi} \right) + {\cos\;\omega\;{t \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}}}\end{bmatrix}}}} \\{= {{{- \left( {A/2} \right)}\sin\; 2\omega\; t} + {\left( {B/2} \right)\begin{bmatrix}{{{- \sin}\; 2\omega\;{t \cdot {\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}}} +} \\{{\left( {1 - {\cos\; 2\omega\; t}} \right) \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}} +} \\{{\left( {1 - {\cos\; 2\omega\; t}} \right) \cdot {\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}} +} \\{\sin\; 2\omega\;{t \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}}\end{bmatrix}}}}\end{matrix} & (3)\end{matrix}$

If it is assumed that cut off frequency f0 is f0<<ω, in the LPF 4105,because the high frequency components are cut off, only the componentsshown in expression (4) are output as signal Sc1.

[Expression 4]Sc1=(B/2)[sin(Δωt+φ)+cos(Δωt+φ)]  (4)

The phase shifter 4106 inputs the signal Sc1, and outputs a signal Sf1,delaying the phase of signal Scd by 90 degrees. Therefore:

[Expression 5]Sf1=(B/2)[−cos(Δωt+φ)+sin(Δωt+φ)]  (5)

The multiplier 4101 multiplies signal Sp and signal Sq. Therefore signalSd1 is:

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 6} \right\rbrack & \; \\\begin{matrix}{{{Sd}\; 1} = {\left\lbrack {{A\;\sin\;\omega\; t} + {B\begin{bmatrix}{{\sin\left\{ {{\left( {\omega + {\Delta\omega}} \right)t} + \phi} \right\}} +} \\{\cos\left\{ {{\left( {\omega + {\Delta\omega}} \right)t} + \phi} \right\}}\end{bmatrix}}} \right\rbrack\sin\;\omega\; t}} \\{= {{A\;\sin\;\omega\;{t \cdot \sin}\;\omega\; t} + {{B\begin{bmatrix}{{\sin\;\omega\;{t \cdot {\cos\left( {{{\Delta\omega}\; t} + \phi} \right)}}} +} \\{{\cos\;\omega\;{t \cdot {\sin\left( {{{\Delta\omega}\; t} + \phi} \right)}}} +} \\{\cos\;\omega\;{t \cdot {\cos\left( {{\Delta\;\omega\; t} + \phi} \right)} \cdot}} \\{{- \sin}\;\omega\; t} \\{\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}\end{bmatrix}}\sin\;\omega\; t}}} \\{= {{\left( {A/2} \right)\left( {1 - {\cos\; 2\omega\; t}} \right)} + {\left( {B/2} \right)\begin{bmatrix}{1 - {\cos\; 2\omega\;{t \cdot \cos}}} \\{\left( {{\Delta\;\omega\; t} + \phi} \right) + {\sin\; 2\omega\;{t \cdot}}} \\{{\sin\left( {{\Delta\;\omega\; t} + \phi} \right)} +} \\{\left( {1 - {\cos\; 2\omega\; t}} \right) \cdot} \\{{\cos\left( {{\Delta\;\omega\; t} + \phi} \right)} +} \\{\sin\; 2\omega\;{t \cdot {\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}}}\end{bmatrix}}}}\end{matrix} & (6)\end{matrix}$

In LPF 4102, if the cut off frequency f0 is f0<<ω, because the highfrequency components are cut off, only the components shown inexpression (7) are output as signal Se1.

[Expression 7]Se1=A/2+(B/2)[cos(Δωt+φ)−sin(Δωt+φ)]  (7)

The adder 4107 inputs and adds the signal Se1 and Sf1, and outputs thesignal as Sr. Therefore, signal Sr is obtained by expression(5)+expression (7):

[Expression 8]Sr=Sf1+Se1=A/2  (8)and, a signal that has only the amplitude of the desired receptionsignal is output. As shown in FIG. 11, because the information includedin the low-frequency standard radio wave is determined by binaryamplitude and pulse width, there is no problem if signal Se is ½ theamplitude of the desired reception signal.

As the above, noise is eliminated from the received radio wave, and onlythe components of the desired reception signal can be output. The LPFs4102 and 4105 are low pass filters for cutting of high frequency wavecomponents, and it is not necessary for the band width to beparticularly narrow. Therefore, because it is not necessary to apply afilter circuit with a particularly narrow band with, to separate noisefrom the received radio wave, time delay occurring by the filter circuitcan be prevented. Additionally, because the noise near the frequency ofthe desired reception signal, such as signals included in the filtercircuit can be eliminated, the reception performance of the radio wavereception device can be improved.

Eleventh Embodiment

In the tenth embodiment, the radio wave reception device comprising thesignal reproduction circuit, applying the phase shifter is described. Inthe present embodiment, a radio wave reception device comprising asignal reproduction circuit, applying a differentiation circuit will bedescribed. The structure of the radio wave clock of the eleventhembodiment has the same structure as the radio wave clock 1 of FIG. 1,in the first embodiment.

The structure of the radio wave reception device is the same structurereplacing the signal reproduction circuit 4010 that constitutes theradio wave reception device 4917 of FIG. 27 to a signal reproductioncircuit 4020 of FIG. 29. Therefore, descriptions for the overlappingparts will be omitted by putting the same reference numerals.

FIG. 29 is a circuit block diagram showing the structure of the signalreproduction circuit 4020. The signal reproduction circuit 4020comprises multiplication circuits 4020C, 4020D, differentiation circuits4203, 4208, adders 4206, 4210, a subtracter 4207, and a (1/Δω) amplifier4209.

The multiplication circuit 4020C comprises a multiplier 4201 and an LPF4202. The multiplier 4201 multiplies the signal Sp input by the filtercircuit 4008 and the signal Sq input by the carrier extraction circuit4009, and outputs the signal as signal Sd2. The LPF 4202 allows apredetermined range (low pass) of frequency components relating to thesignal Sd2 input by the multiplier 4202 to pass through, i.e. outputs asignal Se2, cutting off the frequency components that are out of therange.

The differentiation circuit 4203 carries out differentiation processingof the signal Sp input from the filter circuit 4008, and outputs thesignal as Sa2. The multiplication circuit 4020D includes a multiplier4204 and an LPF 4205. The multiplier 4204 multiplies the signal Sa2input from the differentiation circuit 4203 and the signal Sq input fromthe carrier extraction circuit 4009, and outputs the signal as Sb2. TheLPF 4205 allows signal components having low frequencies, relating tothe signal Sb2 input from the multiplier 4204, i.e. outputs the signalSc2, cutting off the frequency components that are out of the range. Theadder 4206 adds the signal Se2 output from the LPF 4202 and the signalSc2 output from the LPF 4205, and outputs the signal as Sf2.

The subtracer 4207 subtracts the signal Sc2 output from the LPF 4205from the signal Se2 output from the LPF 4202, and outputs the signal asSg2. The differentiation circuit 4208 carries out differentiationprocessing of the signal Sg2 input from the subtracter 4207, and outputsthe signal as Sh2. The (1/Δω) amplifier 4209 multiplies the signal Sh2,which is input from the differentiation circuit 4208, by (1/Δω), andoutputs the signal as Sj2. The adder 4210 adds the signal Sf2 input fromthe adder 4206 and the signal Sj2 input from the (1/Δω) amplifier 4209,and outputs the signal as Sr2.

The signal Sp output from the filter 4008 includes desired receptionsignal and noise components. The frequency of the desired receptionsignal is assumed to be ω, and the signal wave thereof A sin ωt. Here,amplitude A is a time function. Signal Sp can be expressed as expression(9) by mixing the amplitude component A of the desired reception signaland noise amplitude component B.

[Expression 9]Sp=A sin ωt+B[sin {(ω+Δω)t+φ}+cos {(ω+Δω)t+φ}]  (9)

The differentiation circuit 4203 carries out differentiation processingof signal Sp, and outputs the signal as Sa2. Therefore:

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 10} \right\rbrack & \; \\\begin{matrix}{{{Sa}\; 2} = {\frac{\mathbb{d}}{\mathbb{d}t}({Sp})}} \\{= {{\left( {A\;\omega} \right)\cos\;\omega\; t} + {{B\begin{bmatrix}{{\cos\left\{ {{\left( {\omega + {\Delta\;\omega}} \right)t} + \phi} \right\}} -} \\{\sin\left\{ {{\left( {\omega + {\Delta\;\omega}} \right)t} + \phi} \right\}}\end{bmatrix}}\left( {\omega + {\Delta\;\omega}} \right)}}}\end{matrix} & (10)\end{matrix}$

Because Δω<<ω, the expression can be simplified as:

[Expression 11]Sa2=(Aω)cos ωt+(Bω)[cos {(ω+Δω)t+φ}−sin {(ω+Δω)t+φ}]  (11)

Because the signal Sq output from the carrier extraction signal 4009 issin ωt, he signal Sb2 output from the multiplier 4204 is:

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 12} \right\rbrack & \; \\\begin{matrix}{{{Sb}\; 2} = {\left\lbrack {{\left( {A\;\omega} \right)\cos\;\omega\; t} + {\left( {B\;\omega} \right)\begin{bmatrix}{{\cos\left\{ {{\left( {\omega + {\Delta\;\omega}} \right)t} + \phi} \right\}} -} \\{\sin\left\{ {{\left( {\omega + {\Delta\;\omega}} \right)t} + \phi} \right\}}\end{bmatrix}}} \right\rbrack\sin\;\omega\; t}} \\{= {{\left\{ {A\;{\omega/2}} \right\}\sin\; 2\omega\; t} + {{\left( {B\;\omega} \right)\begin{bmatrix}{{\cos\;\omega\;{t \cdot {\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}}} -} \\{{\sin\;\omega\;{t \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}} -} \\{{\sin\;\omega\;{t \cdot {\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}}} -} \\{\cos\;\omega\;{t \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}}\end{bmatrix}}\sin\;\omega\; t}}} \\{= {{\left\{ {A\;{\omega/2}} \right\}\sin\; 2\omega\; t} + {\left( {B\;{\omega/2}} \right)\begin{bmatrix}{{\sin\; 2\omega\;{t \cdot {\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}}} -} \\{\left( {1 - {\cos\; 2\;\omega\; t}} \right) \cdot} \\{{\sin\left( {{\Delta\;\omega\; t} + \phi} \right)} -} \\{\left( {1 - {\cos\; 2\;\omega\; t}} \right) \cdot} \\{{\cos\left( {{\Delta\;\omega\; t} + \phi} \right)} -} \\{\sin\; 2\;\omega\;{t \cdot {\sin\left( {{\Delta\;\omega} + \phi} \right)}}}\end{bmatrix}}}}\end{matrix} & (12)\end{matrix}$

In the LPF 4205, if it is assumed that the cut off frequency f0 isf0<<ω, because the high frequency components are cut off, only thecomponents shown in expression (13) are output as signal Sc2.

[Expression 13]Sc2=(Bω/2)[−sin(Δω+φ)−cos(Δωt+φ)]  (13)

The multiplier 4201 multiplies signal Sp and signal Sq. Therefore,signal Sd2 is:

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 14} \right\rbrack & \; \\\begin{matrix}{{{Sd}\; 2} = \left\lbrack {{A\;\sin\;\omega\; t} + {{B\begin{bmatrix}{{\sin\left\{ {{\left( {\omega + {\Delta\;\omega}} \right)t} + \phi} \right\}} +} \\{\cos\left\{ {{\left( {\omega + {\Delta\;\omega}} \right)t} + \phi} \right\}}\end{bmatrix}}\sin\;\omega\; t}} \right\rbrack} \\{= {{A\;\sin\;\omega\;{t \cdot \sin}\;\omega\; t} + {{B\begin{bmatrix}{{\sin\;\omega\;{t \cdot {\cos\left( {{\Delta\;\omega} + \phi} \right)}}} +} \\{{\cos\;\omega\;{t \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}} +} \\{{{\cos\;\omega\;{t \cdot {\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}}} -}\;} \\{\sin\;\omega\;{t \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}}\end{bmatrix}}\sin\;\omega\; t}}} \\{= {\begin{matrix}\left( {A/2} \right) \\{\left( {1 - {\cos\; 2\;\omega\; t}} \right) +} \\\left( {B/2} \right)\end{matrix}\begin{bmatrix}{\left( {1 - {\cos\; 2\;\omega\; t}} \right) \cdot} \\{{\cos\left( {{\Delta\;\omega\; t} + \phi} \right)} +} \\{{\sin\; 2\;\omega\;{t \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}} +} \\{{\sin\; 2\;\omega\;{t \cdot {\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}}} -} \\{\left( {1 - {\cos\; 2\omega\; t}} \right) \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}\end{bmatrix}}}\end{matrix} & (14)\end{matrix}$

In the LPF 4202, if it is assumed that the cut off frequency f0 isf0<<ω, because the high frequency components are cut off, only thecomponents shown in expression (15) are output as signal Se2.

[Expression 15]Se2=A/2+(B/2)[cos(Δωt+φ)−sin(Δωt+φ)]  (15)

The adder 4206 adds the signal Sc2 and signal Se2, and outputs thesignal as Sf2. The subtracter 4207 subtracts signal Sc2 from signal Se2,and outputs the signal as Sg2. Here, because ω is a constant number,signal Sf2 and Sg2 can be simplified as the below expression.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 16} \right\rbrack & \; \\{{{Sf}\; 2} = {{\frac{{Sc}\; 2}{\omega} + {{Se}\; 2}} = {{A/2} - {B\;{\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}}}} & (16) \\\left\lbrack {{Expression}\mspace{14mu} 17} \right\rbrack & \; \\{{{Sg}\; 2} = {{{{Se}\; 2} - \frac{{Sc}\; 2}{\omega}} = {{A/2} - {B\;{\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}}}}} & (17)\end{matrix}$

The differentiation circuit 4208 carries out differentiation processingof signal Sg2, and outputs the signal as Sh2. Therefore, if expression(17) is differentiated:

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 18} \right\rbrack & \; \\{{{Sh}\; 2} = {{\frac{\mathbb{d}}{\mathbb{d}t} \cdot \left\{ {{A/2} - {B\;{\cos\left( {{\Delta\;\omega\; t} + \phi} \right)}}} \right\}} = {{B \cdot \Delta}\;{\omega \cdot {\sin\left( {{\Delta\;\omega\; t} + \phi} \right)}}}}} & (18)\end{matrix}$

Signal 5112 is multiplied by (1/Δω), by the (1/Δω) amplifier 4209, andthe adder 4210 adds signal Sf2 and signal Sj2. Therefore:

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 19} \right\rbrack & \; \\{{{Sr}\; 2} = {{{{Sf}\; 2} - \frac{{Sh}\; 2}{\omega}} = {A/2}}} & (19)\end{matrix}$and, a signal that has the amplitude of only the desired reception radiowave is output. Here, as shown in FIG. 11, because the informationincluded in the low-frequency standard radio wave is determined bybinary amplitude and pulse width, there is no problem if signal Sr2 is ½the amplitude of the desired reception signal.

As the above, noise is eliminated from the received radio wave, and onlythe components of the desired reception signal can be output. The LPFs4202 and 4205 are low pass filters for cutting of high frequency wavecomponents, and it is not necessary for the band width to beparticularly narrow. Therefore, because it is not necessary to apply afilter circuit with a particularly narrow band with, to separate noisefrom the received radio wave, time delay occurring by the filter circuitcan be prevented. Additionally, because the noise near the frequency ofthe desired reception signal, such as signals included in the filtercircuit can be eliminated, the reception performance of the radio wavereception device can be improved.

Twelfth Embodiment

In the tenth embodiment, a radio wave reception device comprising asignal reproduction circuit employing a phase shifter is described, andin the eleventh embodiment, a radio wave reception device comprising asignal reproduction circuit employing a differentiation circuit isdescribed. In the present embodiment, a radio wave reception devicecomprising a signal reproduction circuit employing a phase shifter and adifferentiation circuit will be described. The structure of the radiowave clock in the twelfth embodiment, is the same as the structure ofthe radio wave clock 1 of FIG. 1. The structure of the radio wavereception device is the same, except that the signal reproductioncircuit 4030 shown in FIG. 30 replaces the signal reproduction circuit4010 that constitutes the radio wave reception device 4917 shown in FIG.27. Therefore, descriptions for the overlapping parts will be omitted byputting the same reference numerals.

FIG. 30 is a circuit block diagram showing the structure of a signalreproduction circuit 4030. The signal reproduction circuit 4030comprises the multiplication circuit 4020C, 4030D, phase shifter 4302,adders 4206, 4210, subtracter 4207, differentiation circuit 4208 and(1/Δω) amplifier 4209. The structure of a block 4020B that includes themultiplication circuit 4020C, adders 4206, 4210, subtracter 4207,differentiation circuit 4208 and (1/Δω) amplifier 4209, is the samestructure as block 4020B of the signal reproduction circuit 4020 of FIG.29.

Block 4030A that includes a multiplication circuit 4030D and phaseshifter 4302, is a modification example of block 4010A of the signalreproduction circuit 4010, shown in FIG. 28. The multiplication circuit4030D comprises a multiplier 4301 and an LPF 4303. Concretely, in block4010A, signal Sa1, where the phase of signal Sp is delayed 90 degrees,and signal Sq output from the carrier extraction circuit 4009 aremultiplied by the multiplier 4104. However, in block 4030A, signal Spand a signal, where the phase of signal Sq is delayed 90 degrees, ismultiplied by the multiplier 4301. Here, the signal output from themultiplier 4104 and the signal output from the multiplier 4301 is thesame. A signal delaying the phase 90 degrees of either the signal Sp orSq, and the other signal Sp or Sq may be multiplied.

Because the expressions showing each signal can be calculated by thesame method as described in the tenth embodiment and the eleventhembodiment, the descriptions will be omitted. However, a signal thatdoes not include noise components, and the amplitude is ½ the amplitudeof the desired reception signal, is output from the adder 4210 as signalSr3.

As the above, noise is emitted from the received radio wave, and onlythe components of the desired reception signal can be output. Therefore,because it is not necessary to apply a filter circuit with aparticularly narrow band with, to separate noise from the received radiowave, time delay occurring by the filter circuit can be prevented.Additionally, because the noise near the frequency of the desiredreception signal, such as signals included in the filter circuit can beeliminated, the reception performance of the radio wave reception devicecan be improved.

Thirteenth Embodiment

In the tenth embodiment, a radio wave reception device comprising asignal reproduction circuit employing a phase shifter is described, andin the eleventh embodiment, a radio wave reception device comprising asignal reproduction circuit employing a differentiation circuit isdescribed. In the present embodiment, a radio wave reception devicecomprising a signal reproduction circuit employing a phase shifter and adifferentiation circuit will be described. The structure of the radiowave clock in the thirteenth embodiment, is the same as the structure ofthe radio wave clock 1 of FIG. 1. The structure of the radio wavereception device is the same, except that the signal reproductioncircuit 4040 shown in FIG. 31 replaces the signal reproduction circuit4010 that constitutes the radio wave reception device 4917 shown in FIG.27. Therefore, descriptions for the overlapping parts will be omitted byputting the same reference numerals.

FIG. 31 is a block circuit diagram showing the structure of the signalreproduction circuit 4040. The signal reproduction circuit 4040comprises multiplication circuits 4010C and 4040D, phase shifter 4106,adder 4107, and a differentiation circuit 4402. The structure of block4010B that includes the multiplication circuit 4010C, phase shifter4106, and adder 4017 is the same as the block 4010B of the signalreproduction circuit 4010, shown in FIG. 28.

Block 4040A that includes a multiplication circuit 4040D and phaseshifter 4402, is a modification example of block 4020A of the signalreproduction circuit 4020, shown in FIG. 29. The multiplication circuit4040D comprises a multiplier 4401 and an LPF 4403. Concretely, in block4020A, signal Sa2, where signal Sp is differentiated, and signal Sqoutput from the carrier extraction circuit 4009 are multiplied by themultiplier 4204. However, in block 4040A, signal Sp and a signal, wherethe signal Sq is differentiated, are multiplied by the multiplier 4401.Here, the signal output from the multiplier 4204 and the signal outputfrom the multiplier 4401 is the same. A signal differentiating eitherthe signal Sp or Sq, and the other signal Sp or Sq may be multiplied.

Because the expressions showing each signal can be calculated by thesame method as described in the tenth embodiment and the eleventhembodiment, the descriptions will be omitted. However, a signal thatdoes not include noise components; and the amplitude is ½ the amplitudeof the desired reception signal, is output from the adder 4107 as signalSr4.

As the above, noise is emitted from the received radio wave, and onlythe components of the desired reception signal can be output. Therefore,because it is not necessary to apply a filter circuit with aparticularly narrow band with, to separate noise from the received radiowave, time delay occurring by the filter circuit can be prevented.Additionally, because the noise near the frequency of the desiredreception signal, such as signals included in the filter circuit can beeliminated, the reception performance of the radio wave reception devicecan be improved.

Various embodiments and changes may be made thereunto without departingfrom the broad spirit and scope of the invention. The above describedembodiments are intended to illustrate the present invention, not tolimit the scope of the present invention. The scope of the presentinvention is shown by the attached claims rather than the embodiments.Various modifications made within the meaning of an equivalent of theclaims of the invention and within the claims are to be regarded to bein the scope of the present invention.

This application is based on Japanese Patent Application No. 2002-301897filed on Oct. 16, 2002, Japanese Patent Application No. 2002-309733filed on Oct. 24, 2002, Japanese Patent Application No. 2002-343534filed on Nov. 27, 2002, Japanese Patent Application No. 2003-30857 filedon Feb. 7, 2003, and Japanese Patent Application No. 2003-30868 filed onFeb. 7, 2003. The disclosure of the above Japanese Patent Applicationsis incorporated herein by reference in it entirety.

1. A radio wave reception device comprising: radio wave reception means which receives amplitude modulation signals; gain control means which outputs gain control signals; amplitude modulation signal amplification means which amplifies the amplitude modulation signal received from said radio wave reception means, according to the gain control signal output from said gain control means; frequency conversion means which mixes the signal output from said amplitude modulation signal amplification means with a predetermined oscillation signal, and outputs the signal as an intermediate frequency signal; intermediate frequency signal amplification means which amplifies the intermediate frequency signal output from said frequency conversion means, according to the gain control signal output from said gain control means; and detection means which detects the signal output from said intermediate frequency signal amplification means, and outputs a detection signal, wherein: said detection means includes; standard signal generating means which generates a standard signal that has the same frequency and same phase as said intermediate frequency signal, based on the signal output from said intermediate frequency signal amplification means, and subtraction means which subtracts said standard signal from said intermediate frequency signal, and said gain control means includes signal level comparing means which compares the signal level of the signal subtracted by said subtraction means with the signal level of said standard level, and said gain control signal is generated according to the comparison result by said signal level comparing means.
 2. The radio wave reception device according to claim 1, wherein said detection means further includes: oscillation means which outputs a signal of a predetermined frequency; phase comparison means which compares the phase of the signal subtracted by said subtraction means with the phase of the signal output from said oscillation means; and a filter that cuts off a predetermined range of frequency components relating to the signal output from the phase comparison means.
 3. A radio wave clock comprising: the radio wave reception device cited in claim 1; time code generating means which generates a standard time code based on a standard radio wave signal included in the amplitude modulation signal received by said the radio wave reception means of this radio wave reception device; timekeeping means which time keeps a present time; and correction means which corrects the present time, time kept by said timekeeping means, based on the standard time code generated by said time code generating means.
 4. A repeater comprising: the radio wave reception device cited in claim 1; time code generating means which generates a standard time code based on a standard radio wave signal included in the amplitude modulation signal received by said the radio wave reception means of this radio wave reception device; and sending means which sends the standard time code generated by said time code generating means. 